NCI Center for Cancer Research, Frederick, MD 21702, USA.
Mol Cell. 2012 Apr 13;46(1):18-29. doi: 10.1016/j.molcel.2012.02.006. Epub 2012 Mar 8.
UV-induced cyclobutane pyrimidine dimers (CPDs) in the template DNA strand stall transcription elongation by RNA polymerase II (Pol II). If the nucleotide excision repair machinery does not promptly remove the CPDs, stalled Pol II creates a roadblock for DNA replication and subsequent rounds of transcription. Here we present evidence that Pol II has an intrinsic capacity for translesion synthesis (TLS) that enables bypass of the CPD with or without repair. Translesion synthesis depends on the trigger loop and bridge helix, the two flexible regions of the Pol II subunit Rpb1 that participate in substrate binding, catalysis, and translocation. Substitutions in Rpb1 that promote lesion bypass in vitro increase UV resistance in vivo, and substitutions that inhibit lesion bypass decrease cell survival after UV irradiation. Thus, translesion transcription becomes essential for cell survival upon accumulation of the unrepaired CPD lesions in genomic DNA.
紫外线诱导的模板 DNA 链中环丁烷嘧啶二聚体 (CPD) 会使 RNA 聚合酶 II (Pol II) 转录延伸停滞。如果核苷酸切除修复机制不能及时清除 CPD，停滞的 Pol II 会为 DNA 复制和随后的转录轮次制造障碍。在这里，我们提供的证据表明，Pol II 具有内在的跨损伤合成 (TLS) 能力，能够在不进行修复的情况下绕过 CPD。跨损伤合成依赖于触发环和桥螺旋，这是 Pol II 亚基 Rpb1 中参与底物结合、催化和易位的两个柔性区域。体外促进损伤绕过的 Rpb1 突变会增加体内的 UV 抗性，而抑制损伤绕过的突变会降低 UV 照射后细胞的存活率。因此，跨损伤转录在基因组 DNA 中未修复的 CPD 损伤积累时对于细胞存活变得至关重要。
